Carburetor



Dec. 8, 1964 E. A. JOHNSON 3, 6

CARBURETOR Filed March 2, 1962 2 Sheets-Sheet 2 INVENTOR. ELDON A.JOHNSON AGENT United States Patent 3,169,683 canennuron V Eldon A. liohuson, Sunset Hiils, Mo, assignor to ACE In- This invention is directed to a carburetor for small engines used with power tools. The application of carburetors of this type is With engine driven devices such as chain saws and other portable power tools as Well as gocarts and outboard motors.

This application is a continuation-in-part of my copending application, Serial No. 152,560, filed on Novem- In applications with engines used with portable power tools, as well as small vehicles, the carburetor is expected to be a rather simple device but yet provide all of the advantages of a more sophisticated carburetor. The power tool is used in all positions and the carburetor must be one which can supply an optimum mixture of fuel and air to the engine under conditions varying from idle speeds to high speeds at wide open throttle. Carburetors of this type, because of the nature of their application, are provided with a built-in fuel pump, which supplies fuel under pressure to a fuel chamber from which the fuel is conducted to the air and fuel mixture conduit of the cmburetor.

The fuel chamber of carburetors of this type may have a flexible wall operatively connected through a valve operating mechanism to an inlet valve for supplying fuel from the pump portion of the carburetor to the fuel chamber. It is necessary that the flexible wall and its valve operating structure be sufficiently sensitive so that under difiering conditions of operation the required amount of fuel will be supplied for proper operation of the engine. The valve operating mechanism must be one which is sufiiciently consistent in its operation so that small changes in pressure within the fuel chamber will be operative to open or close the inlet valve. Thus, the diaphragm valve control mechanism can quickly sense operative conditions within the mixing conduit of the carburetor and respond accordingly to supply more fuel or to close off the fuel supply. Such a sensitive fuel supply will quickly respond to instant demands of the engine upon acceleration to full'speed from a low speed idle condition.

It is thus an object of this invention to provide a novel carburetor of the type described having a built-in fuel pumping system and a fuel chamber which will properly sense the fuel demands of an engine under all conditions of operation. I

It is a further object of this invention to provide a novel carburetor structure having a fuel chamber with a diaphragm operated inlet valve in which the operating structures are sensitive to all demands of the engine.

The invention is directed specifically to a carburetor having fuel pump and fuel chamber portions. The carburetor is provided with a fuel chamber, one wall of which is mova le and'formed by a flexible diaphragm operatively connected to an inlet valve. The operating structure connecting the diaphragm and valve are modified to provide an operating assembly which is sensitive in its operation and which effectively provides sufiicient fuel for all conditions of engine operation.

FIGURE 1 is an elevational view of the carburetor in accordance with this invention and connected to the intake manifold of an engine shown partly in section.

FIGURE 2 is atop plan view of the carburetor of FIGURE 1.

FIGURE 3 is an enlarged longitudinal sectional view of the carburetor of FIGURES 1 and 2 and taken on section line 33 of FIGURE 2.

FIGURES 4 is an enlarged sectional view of the carburetor of FIGURES 1 and 2 and taken on the section line 44 of FIGURE 2.

FIGURE 5 is a plan view of the fuel chamber diaphragm and plate structure of the carburetor of FIG- URES l4 and in accordance with the invention.

FIGURE 6 is a bottom plan view of the carburetor of FIGURES 1-4 with the fuel chamber plate and diaphragm removed to show the interior of the fuel chamber.

FIGURE 7 is an enlarged sectional view of a portion of the carburetor of FIGURES 1-4 showing the main fuel system.

FIGURE 8 is an enlarged sectional View of portion of the carburetor of FIGURES 14 showing the low speed or idle fuel system.

' sion stroke of the engine, the mixture of gas and fuel is bled by a passageway from the engine crankcase into the engine cylinder. During the operation of engines of this type the pressure of the gases within the crankcase of the engine undergoes a change from sub-atmospheric to above atmospheric pressure. These pressure changes are conducted by anappropriate passage to a pumping portion of the carburetor 1b to operate the fuel pump of the carburetor, as described below.

The carburetor shown in the figures of the drawing consists of a main body portion 16, to the underside or bottom of which is attached a fuel chamber cover plate 18 and to the upperside or top of which is attached a pumping chamber cap 29. The carburetor body portion has a flange section 22 which is connected directly to the intake manifold 12 of the engine in any appropriate manner, such as by bolts extending from the intake manifold through the flange 22 with retaining nuts 24 holding the carburetor to the manifold. The pump cap 20 is retained and held to the main body 16 by machine screws 26 threaded into the body 16. In a similar manner the fuel chamber cover plate 18 is fixed to the carburetor body 16 bythreaded screws 27 extendingthrough the plate 1% into threaded portions of the carburetor body.

As shown specifically in FIGURE 3, the carburetor has an air and fuel mixture passage 28 therethrough and in line with an opening into the intake manifold 12 of the engine 14. Mounted within the mixture conduit 28 is a choke valve 39 fixed for rotational movement on a choke shaft 32. Also mounted within the mixture conduit 28 of the carburetor between choke valve 30 and the intake manifold 12 is a throttle valve 34 fixed for movement therewith to a throttle shaft 36 journaled for rotation in the body 16 of the carburetor. Between the choke valve 30 and the throttle valve 34, the mixture conduit 28 is formed with a restriction or venturi portion 38. A reed valve plate structure 40 is mounted between the throttle 34 and the intake manifold 12. The reed valve prevents compressed gases within the crankcase from blowing back through the mixture conduit 28 when the engine exhausts. The intake cycle of the engine sucks air through the mixture conduit 28 of the carburetor and the valve 40 opens at this time. '7

To provide fuel to the engine, the carburetor 11) is formed with a fuel pump structure fixed between the pumping chamber cap 24) and the body 16 of the carburetor. the pumping chamber cap 26 and the carburetor body 16 As shown more clearly in FIGURES 3 and 4, V

are both provided with oppositely disposed cavities or recesses which together form a hollow chamber 44. A pumping diaphragm 42 fixed across chamber 44 divides it into a pumping chamber 46 and a pulsation chamber '48. The attachment of the cap 2%) to the carburetor body 16 by the screws 26 is sufiiciently tight to seal the diaphragm 42 around its peripheral edge between the cap and the body portion 16. A fuel inlet passage St) is formed in cap 20 extending from the fuel chamber 46 upwardly and outwardly to the outer surface of the cap. Within the inlet passage 50 is press-fitted an inlet nipple structure 52 to which may be attached in any appropriate manner a flexible tubing 54 extending to a fuel tank 56, as shown schematically in FIGURE 1. Mounted within the nipple 52 is a tubular mesh structure 53 having an open end press-fitted into the free end of the nipple 52. The other end of the tubular filter 53 is cl sed to the passage of fuel.

An outlet chamber is formed within the pump cap 20 and above the pumping chamber 46, as viewed in FIGURE 4. A flexible valve diaphragm 62 is fixed be tween portions of the pumping cap 20 and a retainer plate 64. The valve diaphragm has partially cutout portions forming a pair of flap valves 66 and 68. Valve 66 is fitted over the inlet passage 56 to provide an inlet check valve for fuel flowing into the pumping chamber 46, "while the valve flap 68 is fitted over a short outlet passage 70 between the pumping chamber 46 and the outlet chamber 60. An aligned portion 72 of retainer 64 provides a stop means for the movement of the inlet valve flap 66 in a downward direction as fuel passes into the pumping chamber 46. In a similar manner, an extension 74 of the cap 20 provides a stop means for the valve flap 68, as it moves in an upward direction for the passage of fuel into the outlet chamber 60, and as viewed in FIGURE'4.

Leading from the outlet chamber 60 is a passage 75 formed in the pumping cap 20 and extending into a second chamber 76 within the cap, which connects with a fuel passage 78 extending downwardly, as viewed in FIG- URE 4, to a fuel chamber 80. Fuel chamber 80 is formed by a depression in the carburetor body 16 which is closed on one side by a flexible diaphragm 82 fastened and sealed between the body casting 16 and cover plate 18. Fitting in the lower end of the fuel passage 78 is valve assembly consisting of a sleeve 84 sealed by an O-ring 86 to the body casting 16. Within the sleeve 84 there is positioned a resilient valve seat 88 retained by a ring 90 press-fitted into sleeve 84. Valve seat 88 may be an annular synthetic rubber Washer into the center of which is fitted one end of a needle valve 92. A threaded fitting 87 locks sleeve 84 within the body 16 and also retains a light spring 89 between its flanged end and the flange of the needle valve 92. The valve 52 has a tapered upper end 94 which has an extension, as shown in FIGURE 4, extending through the annular rubber seat 38. The lower end of needle 92 has a headed end 95 in which is positioned the forked end of a lever 96 pivoted on'a shaft 98 journaled within the body casting 16. The other end of lever 96 is in operative contact with a metallic button 109 fixed to the center of the diaphragm 82. Button 109 consists substantially of a headed rivet, which is used to tightly hold a pair of backing plates 102 and 194 on opposite sides of the diaphragm S2 for retaining the center of the diaphragm substantially rigid. The backing plates 102 and 104 extend close to the peripheral edge of diaphragm 82, but provide an unsupported annular portion or bight 106, between the backing plates and the portion of the diaphragm 82 which is held between the cover plate 18 and carburetor body 16;

A fuel well 108 extends from the fuel chamber 8G to a cross passage 110 extending from outside the carburetor body 16 and as shown in FIGURES 6 and 7. The cross passage 110 is internally threaded at its outer end to receive a threaded adjusting screw 126. The iner end of screw 126 has a sharp tapered point 123 which extends axially along passage 110 and into a tapered portion 112 of the passage. The tapered portion 112 opens into a nozzle chamber 114 having a nozzle fitting 124 press fitted through Wall thereof into the venturi portion 38 of the air and fuel mixture conduit 28 of the carburetor. The nozzle chamber 114 is separated from the main fuel chamber 89 by a cross plug structure 115.

These portions of the carburetor, shown in FZGURE 7, constitute the high speed fuel circuit of the carburetor. Fuel can flow from the chamber 80 through passages 16%, 110 and the restriction112 into the nozzle chamber 114 from which fuel is drawn out through the nozzle 124. The controlling restrictions in this fuel circuit are the space between the adjustment screw end 125 and the tapered passage 112 as well as the nozzle 124. The well 198 and passages 11%) and 114, are relatively large in comparison to these restricted portions of the fuel passage. For example, the passages 19S and 110 are in the order of 0.312", while the restriction 112 has an operat ing diameter in the order of 0.064". The minimum diameter of the passage through the nozzle fitting 124 is in the order of 0.040". The taper on the pointed end of the adjustment screw 126 is in the order of 15 solid angle, while the restriction 112 into which the adjustment screw end 128 is variably adjusted, is in the order of 17 solid angle. Thus, the metering of the fuel flow through the main fuel passage of FIGURE 7 is controlled by the restriction 112 and the nozzle passage. Screw 126 can be adjusted to provide the desired speed of the engine at wide open throttle.

The low speed fuel circuit, or idle circuit, of the carburetor consists of a well structure 117 extending from the fuel chamber 89 into the carburetor body 16, as shown more specifically in FIGURE 8. A cross passage 119 intersects the fuel well 117 and is threaded at its outer end to receive a low speed adjustment screw 122. The low speed adjusting screw 122 has a tapered end 125 extending into a restriction 121 connecting the cross passage 119 with the low speed fuel chamber 116. A solid plug 123 separates chambers 116 and 80. As shown in FIGURE 3, idle fuel port 118 extends between the fuel chamber 116 and the mixture conduit 28 downstream of the throttle 34 in its closed position. Also, a pair of idle air ports 120 extend between the fuel chamber 116 and the mixture conduit 28 upstream of the throttle 34 in its closed position. The restricted portion 121 of the cross passage 119 has a tapered portion into which the end of adjustment screw 122 can be adjustably positioned. When the throttle 34 is closed and the engine is operating at a low speed or idle speed, fuel is drawn from the chamber 7 80 through passages 117 and 119 past the adjustment screw end 125 and through the restricted passage 121 into the fuel chamber 116. Fuel is then drawn from the chamber 116 through the idle port 118 to operate the engine. Screw 122 can be adjusted to provide the desired operation of the engine at closed throttle position.

In operation, cranking of the engine 14 pumps air through the mixture conduit 28 of the carburetor into the intake manifold 12 of the engine; the reed valve 40 being opened under the pumping suction of the engine. Flow of 7 air past the main fuel nozzle 124 with the throttle valve 34 open provides a subatmospheric pressure at the mouth of nozzle 124 due to the venturi effect of the restriction 38. This low pressure at the mouth of nozzle 124 is transferred back through passages 114, 112, 110 and 108 to the fuel chamber 80. Lowering the pressure in chamber 80 causes atmospheric pressure on the outer surface of diaphragm 80 to press the diaphragm inwardly or upwardly, as viewed in FIGURE 4, and to rock the valve lever 96 in a clockwise direction. This positively pulls the needle valve 92 downwardly and the end of needle valve 94 off of the resilient valve seat 88.

Pulsations in the crankcase of the engine are transferred through a passage 49 (FIGURES 3 and 4) to the transferred into pulsation chamber 28.

D pulsation chamber 4%. The pumping diaphragm 42 flexes back and forth under the efiect of the engine pulsations This causes a pumping action in the pumping chamber 46 which sucks fuel from tank 56 through the conduit 54 into the inlet echamber 50 of the carburetor cap 20. Fuel passes into the pumping chamber 46 and out past the outlet check valve 68 into the passages 60, 76 and 78. Continual pumping forces fuel down past the open valve 92 into the fuel chamber 80 and out through the fuel passages 108, 110 and 114 to the nozzle 124. The capacity of the pump section of the carburetor supplies fuel at a higher rate than used by the engine. Accordingly, fuel accumulates in the fuel chamber 80 to fill it and the fuel reacts against the diaphragm 82 to move it outwardly against atmospheric pressure. The fuel pressure in chamber 89 is aided by the valve spring 89 which, as the diaphragm moves away from lever 96, forces the needle upwardly into a closed position in seat 88. In fuel chamber 80, the fuel pressure within the chamber and the valve spring 88 work together against the atmospheric pressure on the outer surface of the diaphragm 82. The fuel pressure in the fuel chamber 88 varies within a small range of values to open and close the needle valve 92.

An idling or low speed operation of the engine takes 34 is at a subatmospheric pressure and a large pressure depression is created at the idle jet opening 118, which pulls fuel from the fuel chamber 89 through passages 108, 110 and the idle chamber 116. Simultaneously sufficient air for mixing with this fuel and to operate the engine at low speed is sucked through the idle ports 120 upstream of the closed throttle 34. This air is pulled into the idle fuel chamber 116 to mix with the fuel coming from the fuel chamber 80. Adjustment of screw 122 is used to provide the optimum fuel and air mixture for idling or low speed conditions.

The pumping structure of the carburetor is modified to provide a more ehicient pump and one which will provide adequate fuel pumping capacity for maximumfuel requirements during engine operation. The cap 28 is formed with the chamber or hollow 76 to provide a large reservoir of fuel between the outlet valve 63 of the pump and the control valve 92 into the fuel chamber. The pumping diaphragm 42 is extended across the reservoir chamber 76 and encloses an arcuate hollow or cavity 79 formed within the body casting 16 (FIGURES 4 and 8). A rivet 81 is press-fitted into the upper portion of fuel passage 78 and the flange head of the rivet is forced downwardly against the pumping diaphragm 42 to tightly seal the diaphragm at this point to the body block 16. Thus, cavity 79 is sealed in a fuel tight manner to trap air therein. Furthermore, the aperture through the pump ing diaphragm 42 and through which the eyelet 81 is forced, is formed somewhat smaller than the outside diameter of eyelet 81 so that as the eyelet is pressed through diaphragm 42, it forces the diaphragm material outwardly to provide an annular wrinkle or bight formation 83. Air trapped within hollow 79 provides a dampening or "an antipulsation chamber. The diaphragm on its pumping stroke moves a column of fuel filling the fuel passages extending from the pumping chamber 4-6 into the fuel chamber 80. This fuel resists the pumping action of the diaphragm and thus tends to cut down and limit its pumping motion or movement. The dampening chamber 9 provides an air cushion which absorbs the pumping pulses and provides a certain give in the liquid fuel so that the pumping diaphragm does not push against a solid column of fuel in its pumping action. This then permits the diaphragm 42 to move against less fuel resistance to a greater extent during pumping. In this manner the antipulsation chamber '79 is very helpful in counteracting the hydraulic shock to the liquid fuel caused by the resistance of passage 78 to fuel. 7

In accordance with the invention, the lever mechanism used for opening and closing the needle valve 2 is designed to operate with greater sensitivity than previous designs of carburetors of this type. The large size of backing plates 1&2 and 164 provide a greater rigidity to the diaphragm 82, which thus does not tend to absorb and dissipate the pressure of the fuel within-chamber 80. A small backing plate 192, for example, would permit the diaphragm to flex outwardly below the large plate 104 and provide space that would absorb fuel entering chamber 81?, which fuel, as it flows out, permits the diaphragm to move without acting on lever 96. A rigid diaphragm senses changes in fuel pressure within chamber 8% more closely. The large backing plates provide a diaphragm assembly then which is much more reactive to the fuel coming in and leaving the chamber and the diaphragm acts more quickly on lever 96 to open the fuel chamber upon demands of the engine.

As shown in FIGURE 5, the plates 102 and 194 are skeletonized or provided with a minimum number of spokes and a maximum amount of space to cut down the weight of the diaphragm assembly. Between cover plate 18 and diaphragm 82 is a hard, flat fiber gasket 85 which has an inner peripheral edge extending inwardly beyond and underlying an adjacent cut-away portion 167 of the carburetor body 16. This edge 105 ofpth'e washer $5 is pressed inwardly by the flanged edge 10% of plate 18 when screws 27 are tightened down. This forces diaphragm 82 upwardly, as viewed in FIGURE 4, into a directed loop or bight 105, which allows freer movement of diaphragm 82 inwardly under the pressure of the atmosphere. The lower plate 192 in the diaphragm as-' sembly may also be formed to aid in maintaining the diaphragm bight portion 1% whereby travel of this free portion lilo of diaphragm 82 past center and reversing the bight is prevented. This may be done by providing a backing plate 102 larger than 104 so that its edge extends beyond that of plate 104,- as shown in FIGURES 7 and 8. This forces the adjacent portion of diaphragm 82 upwardly into the bight 1G6. Maintaining the bight 166 at all times, with the configuration shown, provides a greater response of the diaphragm to fuel pressure changes within chamber 86, since reversal of the bight upon increase in chamber pressure would tend to accommodate fuel entering chamber 80 without a full response of the diaphragm assembly to the increase in'the minimum required for optimum resiliency and response to pressure changes and for maintaining the bight 106. The fuel chamber 8% adjacent to the peripheral edge of bight 1% is cut away, as shown at 107.; This permits a freer flexing of the bight portion 106 and as the diaphragm moves inwardly into the chamber 80, the edge of the bight 1% does not contact the housing body 16.

If the bight portion 106 contacted a surface of body 16 adjacent to 107, the diameter of the diaphragm would be reduced as the diaphragm moved inwardly. Thus, the effective atmospheric pressure on the diaphragm would change and the needle 92 would not open to the extent it would if t e diaphragm were completely free for movement inwardly andoutwardly. V

The bight 106 of diaphragm 82 is thus freely formed.

'This has certain advantages over a diaphragm having a preformed bight, which has a set rigidity formed therein so that the flexing of the diaphragm inwardly and outwardly is resisted to a greater extent than by a freely formed bight. This then permits the diaphragm assembly to bemuch more reactive to small change in pressure within the fuel chamber 89. This coupled with the large lightly constructed backing plates 102 and file provides a very sensitive. diaphragm assembly which has greater response to changes of pressure.

An added feature of the valve control mechanism, shown in FIGURE 4, is the use of the valve closing spring 89 between the valve and the fitting 87. As the chamber 8i fills with fuel, the diaphragm is pushed outwardly against atmospheric pressure and permits spring 89 to seat the valve against the valve seat 88. This action of the spring is in an axial. direction on the valve so that there is no canting or side pressureagainst the valve, which would be caused by an arrangement in which the valve 92 were directly closed by a spring-pressed lever 96, for example. Furthermore, with the lever 96 positively connected to the valve head 95, there is a positive opening of the valve by the diaphragm pressure on lever 96. If, as in some applications, the valve 89 is allowed to open by fuel pressure in passage 78, the opening of the valve becomes sluggish because of the deposit of gum material on the valve seat over a period of time. The positive opening of the valve by lever 95 overcomes any tendency of the valve to stick because of gumming. It has been found with carburetors fabricated in the manner described above that the valve $2 follows very closely the motion of the diaphragm assembly 1%. 1 Thus, small movements of the diaphragm inwardly and outwardly are reflected immediately and positively on the valve 92 to open or close the valve to the amount re It has also been found that.

quired by engine operation. this arrangement of valve g2 and spring 89 eliminates the tendency of the valve to bounce due to engine vibrations. By making spring 89 effective on the small arm of lever 96 a greater mechanical advantage is possible and spring 89 then can be strong enough to effectively close the inlet in valve seat 88 at all times.

The structure thus described for control of fuel entering the fuel chamber 89 is such as to provide immediate response of the fuel supply to engine demands. That is, small changes of pressure within the fuel chamber 80 are instantaneously transmitted to the valve for its:control. Furthermore, the passages 108, 110 and 114 can be made large so that they offer little or no resistance to the fiow of fuel through the main fuel circuit. Thus,

changes in venturi pressures in the venturi region 34 are almost instantaneously reflected through these passages to the fuel chamber 80.

The above described structure of the fuel system of the carburetor lends itself to the operation of the car- 80, the diaphragm is moved upwardly by atmospheric pressure. In this movement the diaphragm must move against the weight of the diaphgram assembly, including the plates W2 and 104, as well as against the weight of the fuel in chamber 80, the weight of lever 96 and the spring bias of spring 89. Thus, it can be seen that to provide a sensitive operating diaphragm assembly, it is to an advantage to keep the weight of the diaphragm assembly small, as Well as the fuel chamber shallow, and the value of the spring 89 should have a strength only sufiicient to close the valve against the pressure in the fuel line 78. Also, if the diaphragm 82 can be maintained as large as possible, the differential pressure between the atmosphere and that of the fuel in chamber 80 will exert a greater force for opening the inlet valve 92.

When the carburetor of FIGURE 4 is operated in an upside-down position, the weight of the diaphragm asphragm assembly must be minimized so that the valve 92 will not be held open until fuel pressure in the chamber operating lever 33, as shown in FIGURE 2.

*1.) is sufficient to lift the diaphragm off the lever 96. The strength of the spring then is such as to withstand the weight of the diaphragm assembly so that a negative pressure in chamber 80 is necessary at all times to open the valve 92. If these conditions are not met, then the fuel in chamber Si will require a pressure above atmospheric to close off the valve 92. fuel within the chamber at greater than atmospheric pressure will flow through the main fuel passages and into the mixture conduit 28 when the engine is not operating. This causes a wetting of the mixture conduit with an excessive amount of raw fuel and results in hard starting of the engine. Also, a positive fuel pressure within .chamber 8% results in an overrich fuel supply during cngine operation and when the carburetor is operated in its upside-down position from that shown in FIGURE 4. The negative fuel pressure within chamber 8% need not be excessive and can be held to within a fraction of an inch of water in pressure by the proper proportioning of the diaphragm assembly and the strength of spring 89. It is also obvious that the lightest metals of sufficient strength and hardness'are utilized in forming the lever 96 and the valve 92.

In accordance with the invention then, the construction of the carburetor in this region of the main fuel passage is such as to provide a fuel passage having a minimum resistance to the movement of fuel through the passage, which results in a quicker response to changes of pressure in the venturi 38. Furthermore, the large, light backing plates and 104 and the formed bight 196 of the diaphragm assembly, as Well as construction of the needle and lever assemblies, provide an instantaneous following or sensing of the fuel pressure changes in chamber 80. All of this construction, then, results in a fuel supply control which is very sensitive and responds accurately to changes in the venturi or idle fuel pressures. This permits an instantaneous response in fuel fiow to the engine upon acceleration, or deceleration, as the throttle is opened or closed quickly. Instant fuel response is necessary in those applications in'which the engine is used in chain saws, gocarts, or such devices.

The choke shaft has fixed thereto a manual choke By the use of this lever, the choke may be closed during cold starting of the engine to provide an enriched mixture of fuel and air. lVhen the engine has started, the choke 'valve is moved to an open position, as shown in FIGURE 3. Also, the throttle valve 34 is operated by means of a manually operable throttle lever 37 (FIGURE 1) fixed to the throttle shaft 36. Normally, the throttle lever 37 is attached to a Bowden cable or operative linkage through an aperture 39 in the lever 37. An adjustment screw 41 is threaded through an embossment of the carburetor body 16 to provide at its threaded end a stop for lever 37. In this manner the amount of closing of the throttle can be controlled to provide a slightly open throttle under certain conditions of low engine speed.

The carburetor structure described above is one which provides a large capacity of fuel in the pumping section. The passages 74, as well as the outlet chamber 69 and chamber 76, provide for the storage of fuel in sufficient quantities so that upon the opening of the valve 92 and with a large fuel demand by the engine, there is stored adjacent to the fuel chamber Sit a sufficient supply of fuel. The pulsation dampening chamber '79 permits the pumping diaphragm 42 to have a greater displacement during the pumping stroke which increases the efficiency of the pump.

The needle seat assembly provides for quick replacement of the needle and its seat by the simple removal of the fitting 36 and dropping out sleeve 84 with the seat. The insertion of a new sleeve 84 and seat are in the reverse order. The end 9 of needle 92 operates within the valve seat aperture of seat 88 continuously during operation. The needle end 94, as shown in FIGURE 4,

This is a disadvantage, sincev is a rod-like construction and provides a means for metering the flow of fuel through the valve seat 38.

I claim:

A carburetor comprising a body, a fuel and air mixture conduit through said body, said body formed with a fuel chamber enclosed at its outer margin by an annular surface portion, said annular surface portion having its inner edge formed by a cut-away wall portion merging into said chamber, a fuel inlet and a fuel passage extending from said fuel inlet to said fuel chamber, an inlet valve in said fuel passage between said fuel inlet and said fuel chamber, said body having a fuel connection between said fuel chamber and said mixture conduit, means for operating said inlet valve including a circular diaphragm portion connected at its periphery to said annular surface portion of said body and across said fuel chamber to form a wall thereof and means connectin said diaphragm portion to said inlet valve, a circular plate coaxially fixed to one side of the center of said diaphragm portion, said plate extending across a major part of said diaphragm portion and having the periphery thereof spaced from said annular body surface portion, and means forming said diaphragm portion between said plate periphery and said circular body portion into a bight extending into said fuel chamber whereby said diaphragm portion can iii flex, said last means including a rigid annular flat washer fixed to the surface of the periphery of said circular diaphragm portion outside of said fuel chamber and forcing said diaphragm periphery against said annular body surface portion to form a seal therebetween, the fiat inner edge of said washer extending inwardly beyond said cutaway Wall portion and underlying said diaphragm bight portion between said plate and said body to direct said diaphragm material into said bight.

References fired in the file of this patent UNITED STATES PATENTS 2,144,017 Gistucci Jan. 17, 1939 2,232,351 Udale Feb. 18, 1941 2,311,827 Hansen Feb. 23, 1943 2,380,983 Mock Aug. 7, 1945 2,448,131 Williams et al Aug. 31, 1948 2,645,062 Senesky July 4, 1953 2,779,576 Morgenroth Ian. 29, 1957 2,984,465 Hazzard May 16, 1961 3,021,792 Johnson et al Feb. 20, 1962 3,030,084 Phillips Apr. 17, 1962 3,045,605 Nutten et a1 July 24, 1962 3,072,390 Phillips Jan. 8, 1963 

